This invention relates to an apparatus and method for improving ventilation in the form of humidity and temperature control especially when applied to the control of moisture in indoor swimming pool environments (natatoriums).
Natatoriums are typically operated at high humidity levels as compared to standard living space to provide creature comfort to wet-bodied inhabitants. This high humidity level (dew point) creates condensation on the surfaces of building components. In addition to being disagreeable aesthetically, the constant presence of condensation promotes the growth of mildew and fungi and may greatly accelerate deterioration of both surface and internal building components.
Natatoriums place two specific demands on a high volume air conditioning (HVAC) system which are unqiue: the system must remove a relatively constant amount of moisture which migrates into the air by evaporation of the pool surface; and
the air system must be equipped to deliver a constant supply of warm/dry air which can be directed toward condensation-prone building components, such as windows.
Humidity control has typically been attempted by implementing standard ventilation systems. In these systems, exhaust/intake fans may be cycled on and off either manually or by "make/break" humidity controllers. This same general approach can be combined with space heating equipment in the form of direct or indirect fired make-up-air systems. Electric, hydronic or steam heaters may also be employed as heat source in make-up-air equipment.
Both versions of the straight ventilation approach to humidity control have serious drawbacks. Because the blowers are either on or off, great swings in humidity and temperature conditions result, especially when both heat and outside air are delivered through the same on/off make-up-air unit. During colder weather the heating demands of the pool space will cause the standard make-up-air system to run longer than would be required to satisfy the moisture removal requirement in order to produce adequate heat. The surplus of outside air causes the humidity level within the pool environment to drop below the comfort level. Even though the heater may keep the air temperature at 80 degrees or more when the relative humidity drops much below 50-60% relative humidity evaporation on the skin of wet bodies using the pool results in the sensation of being cold. This condition may be expected when the relative humidity level drops much below the 50-60% level.
The standard ventilation systems as described above do not have the ability to provide a continuous supply of air to windows and other condensation-prone surfaces. When the system is "on" the airflow is available to "wipe" these surfaces. Between cycles when the system is "off" the airflow ceases and immediately condensation begins to form on susceptible surfaces.
If the fans are kept in operation continuously to establish the desired constant air flow, wide temperature swings will result. In addition this continuous air exchange will drive the relative humidity to extremely low and uncomfortable levels.
One of the worst drawbacks of the standard ventilation systems is the operating cost. Heating 100% make-up-air, especially in colder climates, is completely unacceptable in light of high utility costs.
Some attempts have been made to address the humidity and temperature control requirements of indoor swimming pools with mechanical refrigeration or heat pump equipment. These systems remove moisture by circulating air from the natatorium through a chilled coil whereby water is condensed out of the air stream before it is introduced back into the defined indoor space. These systems typically produce the same fluctuations in temperature and humidity because the method of control is "make/break". There is often a conflict in the operational modes of the heat pump where adequate dehumidification and heat output can not be derived at the same time (so the air becomes either too cold or too wet). Finally these compressor-bearing units require substantial electrical branch circuits to accommodate their relatively large draw of power.
The invention utilizes the simplicity of standard ventilation equipment in that few moving parts are required for operation. The only significant moving parts required for basic operation are two fans and a series of motorized dampers. This does not include the reheat section which may incorporate one of many types of heating sources (hydronic, electric, steam, gas or oil) and may rely on a remote source of heat such as a boiler.
The invention eliminates the temperature and humidity swings typical of any of the "make/break" systems by full modulation of the outdoor air intake/exhaust for humidity control and with full modulation of the reheat coil output.
By incorporating the energy recovery module into the exhaust/intake section of the system, most of the enormous cost of heating outside intake air may be saved.
Because the only significant electrical consumption by the invention is by its two fans, electrical requirements are greatly reduced as compared to compressor bearing refrigeration devices. This does not include the reheat coil which may be electric and therefore would increase the electrical requirement, however, space heating demand due to transmission loss on this coil would be virtually identical in any of the systems described.
The power consumed by the invention to effect the dehumidification process is substantially less than both the ventilation-type systems and the refrigeration-type systems because of the relatively low power requirement of the fan systems and the high efficiency energy recovery module.
Because of the limited number of moving parts and use of electronic controls the invention is reliable with a lower long-term cost of maintenance when compared to compressor bearing refrigeration units. Regular preventative maintenance consists of air filter maintenance and occasional lubrication of fan parts.
The present invention embodies a system and a method of controlling the moisture accumulation, the relative humidity and the temperature in a defined environment such as a natatorium. The moisture removal is effected by exchanging a variable amount of moisture-laden air for drier outdoor (ambient) air. The volume of air required is variable because the dryness of the outdoor air is variable. As the outdoor air gets drier the volume of air exchange required to compensate for the constant pool evaporation is reduced.
Constant indoor airflow which continuously wipes those surfaces prone to moisture accumulation is achieved by integrating the flow of outdoor air with the indoor air and discharging the same at a constant flow rate.
The flow of the outdoor air is modulated, based on the indoor humidity demand and the dryness of the outdoor air to ensure the indoor airflow remains at a constant level.
In a preferred embodiment of the invention, a modulating humidity/sensor control senses the indoor humidity condition and opens/closes exhaust/intake dampers until the humidity condition reaches the setpoint as selected at the humidity control. The exhaust damper is on the pressure-side (downstream) of a return fan which removes the moisture laden air from the environment. Also on the pressure side of the fan is a bypass damper through which flows the moisture laden air not discharged through the exhaust damper.
The intake damper is on the suction-side (upstream) of a supply fan. The intake damper controls the amount of outdoor air entering the system. The outside air and the moisture laden air flowing through the bypass damper are combined in a common plenum in which plenum is disposed a reheat coil on the suction side of the supply fan. This supply fan discharges the air back into the defined environment.
To maintain the indoor airflow through the return/supply loop constant, the fundamental characteristics of centrifugal blowers are applied. For a blower operating at a fixed speed (R.P.M.), the volume of air passing through the blower will be constant for a given static pressure loading across the blower inlet/discharge. That is, if the static pressure across the blowers is controlled at a constant level the airflow through the blower will also be constant.
A sensor reads the pressure differential across the blowers (bypass damper) and operates the bypass damper actuator open/closed to maintain the fixed static pressure reading (as determined by the fan performance curves).
The modulation of the face exhaust/intake dampers would normally tend to build/relieve the static pressure across the bypass damper, which would change the indoor airflow. However, the bypass damper pressure control "follows" the action of the intake and exhaust dampers holding the differential pressure and in turn the indoor airflow is held constant.
During this process heat energy is transferred from the exhaust air to the intake air by using a heat recovery device. This heat recovery minimizes the reheat necessary to bring the incoming dry air up to room temperature.
A reheat coil adds heat to the air in the common plenum to compensate for the space heating requirements as well as to reheat the incoming dry air.
Another desirable feature for indoor pool applications is to maintain the overall static pressure in the defined environment slightly negative with respect to the surrounding living spaces and outdoors. With this slight negative pressure the high-moisture content air is confined better within the natatorium. With a null or positive pressure, moisture tends to migrate outwardly into the surrounding living spaces as well as into building components where it can do damage.
In one alternative embodiment of the invention, a supplemental room static pressure sensor/control is used to ensure a predetermined room negative pressure is maintained. In this alternative embodiment, the exhaust and intake dampers are controlled independently.
As determined by certain design conditions some cooling may be required to maintain the defined environment at acceptable levels. That is, in some circumstances the outside air being drawn into the system may be at a higher temperature than the desired temperature within the room. Therefore, in another embodiment of the invention, by adding supplemental components to the system of the preferred embodiment, cooling of the incoming outside air may be accomplished without using traditional compressor driven mechanical refrigeration equipment.
In the previously described preferred embodiment, the invention relies on the dryness of the outside air to drive the dehumidification process. The system is most effective during dry winter months and/or in areas with relatively dry year-round climates.
In applications where the summertime outside humidity level approaches or exceeds the desired indoor humidity level, humidity control by ventilation becomes impractical, air exchange volumes become excessive. Installation and operating cost, because of increased equipment sizing, is also increased. In addition the required high indoor air flow required may cause noise and discomfort due to turbulence and drafts.
For climates where these conditions are encountered, in still another embodiment of the invention, mechanical refrigeration equipment is integrated into the system in a manner to maximize comfort and minimize energy consumption in all operational modes. Broadly, a refrigeration coil/damper module is combined with the system of the preferred embodiment. This module is joined at the outside air connections of the invention.